Conventionally, among terminals used in a multicarrier adaptive modulation communication system in which a terminal transmitting data selects a modulation scheme for each carrier and transmits data based on information for adaptive modulation sent from a terminal receiving data, a terminal that estimates propagation path information from the preamble of a received signal is commonly known (see, e.g., Japanese Laid-Open Patent Publication No. 2005-252827 (claim 8)). An orthogonal frequency division multiplexing system is commonly known in which a receiving terminal groups subcarriers into blocks each consisting of several subcarriers according to the reception power of subcarriers and reports control information on each block to a transmitting terminal so that the transmitting terminal controls the transmission power of subcarriers in the block based on the control information (see e.g., Japanese Laid-Open Patent Publication No. 2003-152671 (paragraph 0026 and claim 1)).
According to the disclosure in Japanese Laid-Open Patent Publication No. 2005-252827, however, the modulation scheme at data transmission is selected based on propagation path information estimated from the preamble of a received signal. This leads to a problem in that discrete data throughput may deteriorate when the phasing environment at transmission of a preamble signal is different from the phasing environment at transmission of data (hereinafter “discrete data”) to be transmitted after transmission of the preamble signal. According to the disclosure in Japanese Laid-Open Patent Publication No. 2003-152671, control information is transmitted during a period in which the characteristics of frequency selective phasing in a propagation path hardly change, bringing about a problem in that when the characteristics of frequency selective phasing change, sufficient control over transmission power cannot be carried out, thereby inviting the deterioration of discrete data throughput.